Keying



jm., "i, w30.; W HANSELL www@ KEUNG Filed oct. 11, 1953 0m ,90er/HH? INVENTOR C.W. HANSELL ATTORN EY Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE KEYIN G poration of Delaware Application October 11, 1933, Serial No. 693,077

3 Claims.

This invention relates to keying circuits especially adapted for line controlled oscillation generators such as described in my copending applications Serial Number 400,489, led October 18, 1929, and Serial Number 692,092, led October 4, 1933.

More fully, line controlled oscillation generators normally involve only high powered stages and normally, therefore, for keying purposes, high powered, large size, bias or blocking rectiflers would be required. Such rectiers would be objectionable inasmuch as they would be expensive in rst cost and power consumption.

It is the object vof my present invention, therefore, to provide a keying system for high powered tubes which shall require only a low powered relatively inexpensive biasing source. In carrying this object into eiect I make use of my discovery to the effect that while high powered oscillation generators such as line controlled oscillators require a high bias to stop oscillations, a much lower bias sulices to keep the tubes blocked oi after oscillations have stopped. Therefore, by virtue of my improved keying system at the ends of dots or dashes there is momentarily applied a high bias which is then decreased to a lower value for holding the oscillator tubes blocked off. As the high voltage need be applied for only a short interval of time, I have devised a circuit which I shall describe more fully hereinafter in which a relatively low powered high voltage rectifier may be used to particularly good advantage.

In the accompanying drawing I have illustrated in wiring diagram form my improved keying system in which a low powered high voltage rectier is utilized for eectively keying a high powered line controlled oscillation generator.

Turning to the drawing the oscillation generating system which is to be keyed comprises a pair of vacuum tubes 2, 4, each having a cathode 6, a control grid 8 and an anode l0. The output circuit consists of a coil l 2 which may be shunted, if desired, by a tuning condenser and is coupled to the secondary i4 which may feed directly into ,an antenna or into succeeding amplifier stages as desired. The cathodes 6 of the tubes 2, 4 are grounded by ground connection I6. Between the grids there is connected a high frequency impedance I8 in the form of an inductance coil.

To the impedance I8, as described more fully in my copending applications Serial Number 400,- 489, filed October 18, 1929, and Serial Number 692,092, filed October 4, 1933, there is connected a transmission line consisting of a pair of conductors 20, 22 having uniformly distributed inductance and capacity and being placed parallel to each other and relatively closely spaced. The transmission line 20, 22 is preferably made so as to have an overall length of one-quarter wavelength at the desired operating frequency as eX- 5 plained more fully in my copending application Serial Number 692,092, filed October 4, 1933, and

is constructed and shielded as described more fully therein.

Between the midpoint of impedance I8 and 10 ground there is connected a resistance 26 in series,if desired, with an inductance coil 28. The resistance 26 is so chosen as to establish a suitable operating bias upon the grids 8 of the tubes 2, 4. 15

Normally, because of the power output of the tubes 2, 4, a high powered biasing rectifier would be required for keying purposes. However, in accordance with my present invention which I shall now describe in greater detail, a relatively 20 low powered bias rectier may be used for keying the high powered oscillator tubes 2, 4. My impro-ved keying system includes a bias rectifier 30 connected across a condenser 32 through a resistance 34. One terminal of the condenser is 25 connected to the grid side of resistance 26 and the other terminal of condenser 32 is connected to the plates 38, 40 of the keying tubes 42, 44. 'Ihe grids 46, 48 of the tubes 42, 44 are connected by way of lead 50 to key 52 and resistance 54 opera- 30 tively associated with potentiometer 56 in turn energized by suitable rectifier or other source of potential 5S. An intermediate point 60 of the potentiometer 5S is grounded so that upon the closing of switch 52, the potential impressed upon 35 the grids 46, 43 through lead 50 is changed from a small positive potential to a fairly high negative value and conversely when the switch 52 is opened the arrangement is such that the voltage upon the grid 46, 48 changes from a negative value to a 40 small positive value.

By way of example, resistor 26 may be made to have a value of 2,000 ohms, resistor 34 to have a value of 4,000 ohms, condenser 32 to have a value of three microfarads, bias rectier 30 to have a 45 no load voltage of approximately 3,000, the voltage impressed upon the grids 46, 48 to be swung between plus 2.5 and minus 200 volts for keying purposes and the tubes 38, 40 to be so chosen as to have a voltage drop when they rst become 50 conductive of about 1,000 volts. As already pointed out, the tubes 2, 4, because of their large rating would normally require a large biasing rectifier to stop oscillations as a consequence of which the system would be rather expensive 55 in flrst cost and power consumption. However,

I have found that although a rather high bias is required to stop oscillations in an arrangement such asthe long line system including tubes 2, 4, a much lower bias would sufiice to keep the tubes blocked off after oscillations had stopped. Consequently, according to my present invention the keying circuits which I have described so far act in such a way that at the ends of dots or dashes there is momentarily applied to the grids 8 of the tubes 2, 4, a high bias which then decreases to a lower value for holding the tubes 2, 4, blocked off.

Thus, let us assume that the tubes 38, 40 have been rendered conductive. Condenser 32, it will further be assumed has been charged up to 3,000 volts. As soon as the impedance of the tubes 38, 40 has been decreased, assuming a thousand volt drop in the tubes 38, 40 there will momentarily be placed upon the grids 8 of the tubes 2, 4 a negative bias of 2,000 volts which is sufcient to stop oscillations. Thereafter in the steady state of stopped oscillations the voltage drop across the 2,000 ohm resistor 26 will decrease to about 700 volts, the bias rectifier 30 being prevented from supplying heavy currents by the action of the 4,000 ohm resistor 34. With such an arrangement the steady state power of the rectifier 3U need only be about a third of the power which would be required if the condenser-resistor combination 32, 34 were not used.

When switch 52 is closed, a negative bias of about 200 volts is impressed upon the grids 46, 48 of tubes 38, 40 blocking those tubes to cut-off. As a consequence, no appreciable voltage is fed from the bias rectifier 30 to the grid leak resistor 26 and the tubes 2, 4 will start oscillating and in the oscillating state the voltage drop across the resistor 26 due to grid rectification may become about 800 volts.

Inductance 28 may be added if desired or omitted. If added it will serve to prolong the period in which the high potential from the condenser 32 is impressed upon the grids 8 of tubes 2, 4.

To again go back to the time when a negative voltage is impressed upon the grids 46, 48 of the tubes 38, 40, the condenser 32 is again charged up through resistance 34, but inasmuch as the condenser 32 takes little power, it aids in reducing the size of the bias rectifier which would normally be required.

Having thus described my invention what I claim is:

1. In combination, a multi-electrode tube having a control electrode and a cathode, a fixed resistance connected between the control electrode and cathode of said tube, a source of biasing potential, the serial combination of a resistance and condenser connected across said source of biasing potential, a connection from the junction between said serial resistance and condenser to the fixed resistance connected between the control electrode and cathode of said tube, and, an impedance the value of which may be varied connected between the other side of the condenser and said cathode of said tube.

2. In combination, a high frequency tube having an anode a cathode and a grid, a high frequency circuit connected between the anode and cathode of said tube, a resistance connected between said grid and cathode, a low powered high voltage source, a resistance connected between the grid end of said first mentioned resistanceand one terminal of said high Voltage source, a condenser connected between the junction of said resistances and the other terminal of said high voltage source, a multi-electrode device having anode cathode and grid electrodes, the anode and cathode electrodes of said device being connected between said other terminal of said source and the cathode of said tube, and means for abruptly changing the potential on the grid electrode of said device with respect to the cathode electrode of said device.

3. In combination, a vacuum tube having anode cathode and grid electrodes, a high frequency circuit connected between said anode and cathode electrodes, a resistance and an inductance coil serially connected between said grid and cathode electrodes, a relatively high voltage low powered source of potential, a resistance connected between one terminal of said source and the grid end of said first mentioned resistance, a condenser connected between the junction point of said resistances and another terminal on said source, an electron discharge device having plate grid and filament electrodes,

said device having its plate connected to said f last mentioned terminal of said high voltage source and its filament electrode connected to the filament of said tube, and means for abruptly changing the potential on the grid of said device with respect to the filament of said device from a small positive potential to a relatively high negative value.

CLARENCE W. HANSELL. 

